Resistance welding system with a self-contained close-loop cooling arrangement

ABSTRACT

A resistance welding system with a self-contained close-loop cooling arrangement which includes a chiller, a welding transformer, a cable and a welding gun. The chiller has a feed-port and return-port for the cooling fluid. The welding transformer has an inlet and outlet for a defined cooling path and the inlet is coupled with the feed port of the chiller while the outlet is coupled with the return port of the chiller. One end of the cable is connected to one side of the transformer, for carrying the welding current. The cable is capable of being coupled to the chiller in a manner to internally transfer the cooling fluid in either direction. The welding gun is connected to the other end of the cable and has a pair of electrodes for applying the current through a pair of workpieces. The welding gun also has a built-in cooling system which is capable of receiving, circulating and returning the cooling fluid to the chiller without external fittings and hoses.

This application is a divisional of U.S. Pat. No. 5,742,022.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an industrial workcell systemand method, and, more particularly, to an all-electric industrialworkcell using no plant-provided facilities suitably adapted for use inresistance welding operations.

2. Discussion of the Prior Art

An industrial or manufacturing workcell is generally provided in a plantor factory for performing various processing tasks on or to material orworkpiece conveyed to the workcell. Exemplary industrial operationsinclude welding (including resistance welding), piercing, mechanicalfastening (e.g., riveting), forming operations, machining operations,material handling operations, assembly operations, hemming operations,adhesive application operations, and cutting operations (e.g., by way oflaser systems). A key attribute associated with such a workcell is, ofcourse, performance. However, since there are generally many differentways in which to implement any particular industrial operation,distinguishing key factors often also include cost (including start-upand maintenance), maintainability of the cell (e.g.,availability/adaptability of replacement parts), and up time(alternately referred to as "down time"). Furthermore, industrialworkcells generally include a variety of processing equipment from avariety of vendors, thus making inter-operability an issue. Inparticular, for large manufacturing concerns (e.g., an automotivemanufacturer), the design and implementation of such industrialworkcells are often delegated to "systems integrators," who take themanufacturers basic workcell specification, and then design, build, andtest the workcells. The verified workcells are then torn-down,transported, and rebuilt at the large concerns' manufacturing site. Inan increasingly competitive marketplace, investigation into improvingindustrial workcells to meet key attributes, such as performance, cost,maintainability, and down time, has been, generally, on a piece meal(i.e., individual component or subassembly) basis. Accordingly, theprior art has not seen significant and substantial improvements vis avis the above-mentioned attributes.

To provide a more concrete idea of the direction taken and resultingshortcomings of the prior art, reference is now made to FIG. 1. FIG. 1shows a prior art industrial workcell 10 adapted for industrialresistance welding operations. Workcell 10 includes a station panel view12, a power and interface panel (PIP) 14, a robot controller 16, a robot20 associated with robot controller 16, a welding transformer 22, aplant-provided compressed air manifold 24, a plant-provided coolingwater feed manifold 26, a plant-provided cooling water return manifold28, an air cylinder 30 mounted on a wrist of robot 20, a welding gun 32coupled with air cylinder 30, and a welding current cable 34 couplingthe welding gun 32 to a secondary side of transformer 22. Workcell 10further includes a clamping tool 36, including a plurality of compressedair-actuated clamps 37 for securing the workpieces to be welded togetherin a predetermined fixed relationship with each other and relative tothe fixed base.

FIG. 2 shows a generally enlarged view of the portion of FIG. 1 enclosedby dashed lines. In particular, note the large number of compressed airhoses 38, and cooling water feed and return hoses 39. It should beappreciated by those skilled in the art that the compressed air isprovided for actuating air cylinder 30 to operate welding gun 32 (i.e.,close and apply clamping force), and air clamps 37, while cooling waterprovided by manifolds 26 and 28 is provided for cooling power switchingdevices in weld control 18 (e.g., silicon controlled rectifiers--SCR),transformer 22, secondary (high current) cable 34, and welding gun 32,particularly the welding electrodes or tips included thereon.

There are a host of shortcomings associated with workcell 10. Foremostperhaps is the unreliability, or, in other words, the "down time"exhibited by such a configuration. It has been observed that over 80% ofthe down time of a workcell of the type shown in FIG. 2 can beattributed to the host of air hoses 38, and feed and return coolingwater hoses 39. The necessity for such hoses, of course, derives fromthe use of conventional air cylinders/cooling designs, which relyexclusively on plant-provided facilities. The material costs of thevarious hoses, pipes, valves, etc. is tremendous. Furthermore, the laborcosts for configuring robot 20 with the various hoses 38, 39, and theassociated pipes, valves, etc. (i.e., "dressing" the robot), due to theemployment of various skilled trades (such as pipefitters, plumbers,etc.), is likewise tremendous. Further, it should be particularlyapparent that the "build" time is significantly increased, thus causingan increase in the delivery time of such a workcell to the commissioningmanufacturer. Support hardware required for use of plant-providedcooling water, and compressed air, such as a surge tank and dense pack(i.e., required for control of the air cylinders), further escalate thematerial cost of workcell 10.

Another cost associated with workcell 10 relates to its uniqueness vis avis other similarly-configured workcells in a plant environment. Itshould be appreciated that each workcell, necessarily, is a uniqueconfiguration, due to the fact that each length of hose, each bend in apipe or conduit, and each selected placement for various cooling waterfittings is necessarily tailored to the particular workcell. It shouldbe further appreciated that the kinematics of the host of hoses(pejoratively referred to as "spaghetti") cannot be accurately predictedor modelled. Accordingly, the robot movements in each workcell must beinputted on-site, step-by-step, to ensure that hoses do not becomeentangled. To further exacerbate this problem, the resulting "windows"in which a robot arm may move through in order to reach, for example, aweld point, is significantly reduced, due, again, to the proliferationof the compressed air and water hoses 38, 39. In a manufacturing planthaving a large number of workcells, the aggregate cost in having toindividually configure each workcell is staggering.

It should be appreciated, however, that the shortcomings of prior artworkcell 10 do not relate solely to cost, maintainability, andreliability, but rather, also extend to the performance of workcell 10.For example, reduced "window" openings restrict path choices for robotarm entry to the workpiece, thus increasing the time to process theworkpiece. Further, the use of air cylinders, such as cylinder 30,restrict the jaw opening choices for weld gun 32. In particular, use ofan air cylinder generally provides either open/close operation, or wideopen/intermediate open/closed operation. Thus, as shown in FIG. 2, theconventional configuration may only provide for two jaw openings havingopening widths of A and B. This inflexibility leads to increasedprocessing time. For example, to clear an obstruction that is onlyslightly greater than distance A, when moving from one weld point to thenext weld point, the jaw opening of gun 32 must be opened to its wideopen position, tip separation distance B. It should be apparent thatthis inflexibility manifests itself in an increased processed time, asextra time is needed to both open the jaw to the wide open position, andthen to close the jaw upon arrival at the next weld spot to its closedpositioned. Moreover, performance as it relates to weld quality if alsounsatisfactory in workcell 10. Particularly, a clamping force applied bygun 32 is an important factor in producing a quality weld on astatistically consistent basis. Due to limitations in the inputcompressed air pressure, the crude pressure regulation by the densepack, and other factors (e.g., pressure drops in hose runs), clampingforce cannot be controlled very accurately. The upshot of this inherentlimitation regarding clamping force is that destructive-testing must beperformed to verify welding operations from time-to-time (i.e., weldedworkpieces must be physically torn apart to determine, for example,break-away force, and weld nugget quality). Finally, each air clamp 37requires an individual I/O port, thus increasing the interface size, andthe associated wiring requirements. The compressed air-actuated airclamps 37 cannot be linked, as by some type of bus architecture (e.g.,manufacturing automation protocol--MAP) since the associated controlvalves and the like are not amenable to such control.

Of course, many of these shortcomings are not limited to an industrialresistance welding operation; for example, a piercing operation relieson plant-provided hydraulics. Accordingly, such an industrial processalso requires the above-described host of connecting hoses/valves andthe problems associated therewith.

Accordingly, there is a need to provide an improved industrial workcellto process a workpiece or workpieces, such as a workcell adapted for aresistance welding operation, that minimizes or eliminates one or moreof the problems as set forth above.

SUMMARY OF THE INVENTION

This invention generally provides an industrial workcell for processinga workpiece such that usage of preselected plant-provided facilities areeliminated. The general methodology derives from eliminating devicesrelying on plant-provided facilities for operation, such as compressedair, cooling water, and pressurized hydraulic fluid, and providing insubstitution all-electric devices in the workcell to implement thedesired industrial operation. A method of controlling an industrialworkcell to process a workpiece in accordance with the present inventionincludes three basic steps. The first step involves fixing the workpiecein a predetermined location using electrically-actuated clamps whereinplant-provided compressed air is not used. The second step relates toselecting one of a plurality of industrial operations. The operationsmay include, welding, piercing, mechanical fastening, forming, andmachining. The final step involves controlling an electrically-actuatedelectronically-controlled device to perform the selected industrialprocess on the workpiece fixed in the predetermined location whereinplant-provided facilities, such as compressed air, cooling water, orpressurized hydraulic fluid, are not used.

Preferably, the method of controlling an industrial workcell relates toa resistance welding operation. The step of fixing the workpiece in apredetermined location using electrically-actuated clamps includes thesubsteps of positioning a second workpiece in a predeterminedrelationship with the first workpiece, and then, fixing the first andsecond workpieces in the predetermined location using theelectrically-actuated clamps. The electrically-actuated device is anelectrically-actuated actuator assembly mounted on a wrist of a robotand is coupled to a welding gun assembly. The welding operation includesthe step of controlling the actuator assembly to position the weldinggun for welding at a selected position and further controlling theactuator assembly to apply a predetermined clamping force. The workcellalso preferably includes self-contained closed-loop cooling means forcooling the high current components, such as the welding gun, a weldingtransformer and the secondary current cable(s) therebetween. Theoperation of the workcell is controlled such that no plant-providedfacilities (i.e., here, no compressed air nor cooling water) are used.By providing an all-electric workcell, the need for plant-providedfacilities are eliminated, thus eliminating the associated water and airhoses and associated support hardware. The material cost of a workcellfor resistance welding in accordance with the present invention isreduced by 30-35%, as compared with conventional technology. Moreover,labor costs in installing the workcells are also significantly reduced.Significant improvements in reliability, attributed mainly toelimination of many of the water and air hoses, has been realized forthe preferred embodiment. Further, delivery time, in absolute terms, hasalso been significantly reduced.

In another aspect of the present invention, an apparatus for securing aworkpiece using a control signal is provided. An apparatus in accordancewith this aspect of the invention defines a tool, which includes a baseportion adapted to receive the workpiece, and plurality ofelectrically-actuated clamps connected to the base and responsive to thecontrol signal for fixing the position of the workpiece relative to thebase. Actuation of the clamps is controlled electrically by wire, ratherthan by way of compressed air using control valves, air hoses, aircylinders and the like. Although each clamp may be allocated its own I/Oport in an industrial control system (e.g., a PLC I/O port), it ispreferably contemplated that the clamps be electrically coupled seriallythrough a data highway wherein each clamp has associated therewithdetection means responsive to the control signal for detecting arespective address and for actuating, in response thereto, the addressedelectrically-actuated clamp to fix the position of the workpiece.

In a third aspect, a method related to the apparatus for securing aworkpiece is provided. The method includes five basic steps. The firststep involves assigning an address to each clamp. Next, selecting one ofthe clamps for actuation. The third step involves formatting the controlsignal to include the address associated with the clamp desired to beactuated. Next, broadcasting the control signal to each clamp throughthe data highway. Finally, the fifth step involves providing actuationpower to the clamp selected in the second step upon receipt of thecontrol signal containing its address.

In a fourth aspect of this invention, a novel clamp is provided thatcontains four major components: a housing, a shaft, a clevis, and a linkmember. The shaft is rotatably disposed in the housing. The clevis isslidably mounted to the housing for motion along a longitudinal axis.The link couples the linear motion of the clevis to the angular motionof the shaft; accordingly it is rotatably connected to both clevis andshaft. Movement of the clevis thus effects rotation of the shaft.

In a fifth aspect of this invention, an improved weld gun assembly foruse in a resistance welding system having electrical actuation isprovided. The improved weld gun assembly includes four major components,a welding gun, a force detection means, an electrically-actuatedelectronically-controlled actuator means, and a control means. Thewelding gun has a pair of electrodes continuously separable through apredetermined range for providing welding current through a pair ofworkpieces to form a weld. The force detection means is preferably aload cell and is operatively coupled to the welding gun for detecting aforce being applied between the electrodes and for generating a signalindicative of the detected force. The actuator means is operatively andmechanically coupled to the weld gun for moving the electrodes to anyone of a plurality of electrode separation distances in a continuousfashion within the predetermined range. Finally, the control means iscoupled to the actuator means and is provided for controlling theactuator in accordance with predetermined criteria including a selectedone of said electrode separation distances. Particularly using the forceindicative signal for controlling the actuator to move the electrodessuch that a predetermined clamping force is applied therebetween.

In a sixth aspect of this invention, an improved resistance weldingsystem having self-contained, closed-loop cooling is provided. Thesystem includes four major elements: a chiller, a welding transformer, acable, and a welding gun. The chiller is associated exclusively with thewelding system (not a plant-provided facility) and is provided forremoving heat from cooling fluid. The chiller has a feed port and areturn port for the cooling fluid. The welding transformer includes afirst inlet and outlet The first inlet is coupled to the feed port, andthe first outlet is coupled to the return port of the chiller. The cableis coupled to the transformer and is provided for carrying secondarywelding current to the welding gun and may take a variety of formsdepending upon the particular configuration of the workcell (e.g., a"hip" mount configuration, a transgun configuration, or a remote mountedtransformer for a "hard" (fixed) tool weld configuration). Common toeach of these configurations, however, is that the cable includes meansfor transferring cooling fluid without external cooling fluid fittingsand hoses. In a "hip" mounted transformer configuration, the cable is akickless cable having two flow paths: a feed path, and a return path.The welding gun, in a like manner, has a variety of configurationsdepending the workcell configuration; however, the unifying attribute ofeach welding gun is that each includes means for receiving cooling fluidwithout external cooling fluid fittings and hoses. In a welding systemhaving a "hip" mount configuration, the welding gun includes at leastone internal cooling channel having an inlet and an outlet coupled tothe cable for cooling its electrodes. The feed path of the cable beingconnected to the gun inlet (by way of a jumper cable), and the returnpath of the cable being coupled to the gun cooling fluid outlet (by wayof a jumper).

These and other features and object of this invention will becomeapparent to one skilled in the art from the following detaileddescription and the accompanying drawings illustrating features of thisinvention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagrammatic and block diagram view of a priorart industrial workcell adapted for use in resistance weldingoperations.

FIG. 2 is an enlarged view of the portion of FIG. 1 enclosed by a dashedline, showing particularly a robot encumbered by a proliferation ofcompressed air, and feed and return cooling water hoses as dictated byreliance on plant-provided facilities.

FIG. 3 is a simplified diagrammatic and block diagram view of apreferred resistance welding workcell embodiment of the presentinvention.

FIG. 4 is an enlarged view of the portion of FIG. 3 enclosed by aphantom line, showing particularly a robot unencumbered by aproliferation of compressed air, and feed and return cooling watermanifolds and hoses.

FIG. 5 is a simplified cross-sectional view of theelectronically-controlled electrically-actuated device for performing aselected industrial operation shown in FIG. 4.

FIG. 6A is a simplified side view of an exemplary welding gunillustrating basic mechanical operation and feed and return coolingfluid ports.

FIG. 6B is a simplified cross-sectional view illustrating how a jumpercable mates with a welding gun without the use of any external coolingfluid fittings or hoses.

FIG. 6C is a simplified cross-sectional view illustrating how a two-wayfluid flow kickless cable mates with a fixed portion of a welding gunwithout the use of external cooling fluid fittings or hoses.

FIG. 6D is a simplified side view of a welding gun illustratingparticularly an o-ring structure.

FIG. 6E is a simplified, exaggerated perspective view of the two-wayflow kickless cable shown in section in FIG. 6C.

FIG. 6F is a simplified cross-sectional view, not to scale, taken alongline 6F--6F of FIG. 6E illustrating feed and return paths foreliminating return hoses.

FIG. 6G is a top view of the welding gun of FIG. 6A.

FIG. 6H is an enlarged view of a portion of a fluid connecting ribbon,illustrating two fluid channels.

FIG. 7A is a broken-away and partially sectioned side view of anelectronically-controlled electrically-actuated clamp in accordance withthe present invention.

FIG. 7B is a simplified top view of the clamp of FIG. 7A.

FIG. 7C is a simplified front view of the clamp of FIG. 7A.

FIG. 7D is a partial exploded view, showing side view of the clevis,link, shaft, and housing portions of the clamp depicted in FIG. 7A.

FIG. 7E is a partial exploded view, showing front views of the clevis,link, shaft, and housing portions of the clamp depicted in FIG. 7A.

FIG. 8 is a simplified schematic and block diagram view of the controlcircuit used to control the electronically-controlledelectrically-actuated device depicted in FIG. 5.

FIGS. 9A, 9B, and 9C is a simplified diagrammatic view illustrating top,left-side, and front views of a chiller referred to in FIG. 4.

FIG. 10 is a simplified diagrammatic and schematic diagram view of thechiller of FIG. 9.

FIG. 11 is a flow-chart diagram view indicating the steps performedduring the operation of the preferred resistance welding workcellembodiment of FIG. 3.

FIG. 12 is a simplified flow-chart diagram view of the steps performedby the actuator control circuit shown in FIG. 8 during the operation ofthe resistance welding workcell embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIG. 3 shows anindustrial workcell 40 for performing one of a plurality of industrialoperations on or to a workpiece such that usage of preselectedplant-provided facilities is eliminated. Preferably, workcell 40 isadapted to perform a resistance welding operation, although it should beappreciated that other industrial operations may be selected and remainwithin the spirit and scope of the present invention. Workcell 40includes an industrial general purpose programmable digital computer 42,a station panel view 44, a power and interface panel (PIP) 46, a controland input/output rack 47, a robot controller 48 having an associatedrobot controller input 49, an industrial manipulator or robot 50, anelectronically-controlled electrically-actuated device 52 for performinga selected industrial operation, means 53 for securing a workpiece usinga control signal including an electronically-controlledelectrically-actuated clamp 54, workpiece 56, actuator control 58 havingan associated actuator control input 59, a weld control 60, a primarycurrent connection 62 coupled to weld control 60, a weld transformer 64,a secondary cable 66, and means 68 for chilling welding cooling fluid.

Computer 42 is included in workcell 40 for providing an interface tocontrol and I/O rack 47. In a constructed embodiment of the presentinvention, workcell 40 is controlled by a programmable logic controller(PLC) program using ladder logic. It is preferably contemplated,however, that workcell 40 be controlled using one of the many PLCreplacement systems commercially available. Generally, a centralprocessing unit (CPU) card associated with a PLC system is programmedusing ladder logic type software to control the system by way of, forexample, an I/O card in rack 47. The PLC replacement system replaces theCPU card with a remote interface card. The general purpose computer 42houses a bus controller card in one of its slots. Software is thenexecuted on the computer 42, which, by way of the bus controller card incomputer 42, and the remote interface in the rack 47, controls variouscomponents of workcell in a manner similar to that of the PLC type CPUcard. However, the software used to program the control of the workcellin the PLC replacement systems, (generally a flow-charting softwarelanguage) is much easier to implement and debug than ladder logic.Moreover, in general, these PLC replacement systems have far greaterdiagnostic capabilities than those found in conventional PLC systems.

Particularly, general purpose computer 42 may be an AST model P-90computer, a Pentium processor based system including 16 megabytes ofrandom access memory (RAM), a 400 megabyte hard drive, and including aMitsubishi Diamond 21T monitor.

The PLC replacement software preferably contemplated for inclusion inworkcell 40 is a package called the Visual Logic Controller™, version1.21, by Steeplechase Software, Inc., of Ann Arbor, Mich. 48106. TheVisual Logic Controller™ is a Windows™-based software package, and, asdescribed above, replaces three separate devices: the PLC centralprocessing unit (CPU), the PLC programming terminal, and an operatorinterface panel. The Visual Logic Controller™ includes flow-chartprogramming, an easy access tool box of development tools, support formultiple Windows™, and project management tools. The card housed in aslot of computer 42 that cooperates with the Visual Logic Controller™may be a G.E. Genius bus controller-type card while the remote interfacecard in the rack 47 may be a G.E. remote I/O scanner card, assuming aG.E. Fanuc rack system is used. It should be understood, however, thatthe Visual Logic Controller™ may be used in conjunction with other I/Omodules in rack 47 from other sources (e.g., Allen-Bradley, APCSeriplex, etc.).

Station panel view 44 is included in workcell 44 for providing anindication of the status of selected operations/logic states. Panel view44 is conventional.

PIP 46 provides a main interconnect point for many of the devices andcontrols included in workcell 40. In particular, for example, robotcontroller 48, and actuator control 58 derive operating power from PIP46. Furthermore, robot controller 48, actuator control 58, and weldcontrol 60 may communicate, with each other by way of interconnects inPIP 46.

Control and I/O rack 47 is preferably of the type employing a G.E. FanucSeries 90-70 backplane format. It should be appreciated, however, thatother systems, such as Allen-Bradley, and APC Seriplex, to name a few,are completely equivalent for purposes of this invention. As mentionedabove, workcell 40, as an interim measure, is controlled by a PLC basedCPU card located in rack 47. However, it is preferably contemplated thata PLC replacement system, particularly Steeplechase Software's VisualLogic Controller™, be used in lieu of the PLC type CPU control. Othercards which may be included in rack 47 include a Genius bus controllercard, a remote I/O scanner (RIO) card, and a plurality of input/output(I/O) cards. In particular, the bus controller card may be provided in ahead-end rack and provide a serial interface to remote I/O rackscontaining an RIO card. That is, there may be several racks in workcell40. The head-end rack includes the CPU (or PLC replacement equivalent)card, and the bus controller card. The far-end or remote I/O racks eachinclude an RIO card. A link is made from the head-end rack to a firstone of the remote I/O racks (from bus controller to RIO card). The RIOcard in the remote rack is then daisy-chained to an RIO card in a secondI/O remote rack, and so on. In this way, multiple racks of I/O cards maybe provided in the system to accommodate particular I/O sizerequirements.

Robot controller 48, robot controller input 49, and robot 50 areprovided for moving electrically-actuated device 52 relative toworkpiece 56 to, for example, make spot welds in a plurality oflocations across the workpiece 56. In the illustrative embodiment, robot50 may be a robot model SA 130 by Nachi Robotic Systems Inc., Novi,Mich. 48375. Relevant operating characteristics of SA 130 include a 130KGF wrist loading weight, 50 KGF forearm loading arm, 6 degrees offreedom, and repeatability to ±0.3 mm. Nachi SA 130 robot 50 is matchedby a Nachi AR controller 48 having an associated input pad 49 forprogramming movements and other functions conventionally programmed intoa robot. FIG. 4 shows an enlarged portion of FIG. 3 enclosed by phantomline. As shown clearly in FIG. 4, robot 50 includes a manifold portion69 for routing cooling fluid from chiller 68 to weld transformer 64, andelectrically-actuated means 52. Robot controller 48 may be programmed toperform a welding cycle. A welding cycle being defined by apredetermined number of welds, a position associated with each weld, aweld schedule (to be performed by control 60), and a actuator schedule,which will be explained in more detail below.

Electrically-actuated electronically-controlled means 52 is providedgenerally for performing any one of a plurality of selected industrialprocesses. With continued reference to FIG. 4, electrically-actuatedmeans includes an electrically-actuated electronically-controlledactuator device 70, and an industrial tool 72, which is preferably awelding gun 72. Device 70 provides improved functionality that improvesperformance of workcell 40, particularly, the ability to accurately andrepeatably applying a predetermined force, and further, to provide themeans, operatively coupled to weld gun 72, for moving electrodes of thegun to any one of a plurality of electrode separation distances within apredetermined range. Particularly, as shown in FIG. 4, assume that thedistance designated by C is the predetermined range of gun 72. Actuatorassembly 70 provides the means for moving the electrodes of gun 72 toany one of a plurality of electrode separation distances within range C.In other words, actuator assembly 70 provides the means forsubstantially continuous variation of the separation distance of theelectrodes. This provides substantially improved flexibility, ascompared to the prior art air cylinder 30/welding gun 32 as shown inFIG. 1, which only permits full-closed/full-open operation, or at best,full-closed intermediate open/full open operation (i.e., discreteseparation distances, as opposed to continuously-variable separationdistances). The advantages arising from this continuously-variableseparation distance features is the ability to tailor welding gun 72 jawopening to the workpiece being welded to avoid obstructions so as tominimize unnecessary jaw movement, which only serves to increase thetime required in the welding process.

Referring now to FIG. 5, a cross-sectional view of the actuator device70 is shown. Preferably, actuator device 70 is a model M200 AX, SN106,by Aura Systems, Inc. El Segundo, Calif. Functional specifications ofactuator device 70 include programmable clamping force of up to 1500pounds, full stroke length of three inches, idle-to-weld position (1inch)--maximum time travel no greater than 250 miliseconds,communication compatibility with existing, conventional centralcontrollers, and a size comparable to existing pneumatic (air)actuators. Actuator 70 includes DC motor 74 having shaft 75, electrodemagnetic clamp 76 including stator 78, coil 79, rotor 80, and gap 81,cover 82, shoulder bolts 83, Acme screw 84, key 85, frame 86, shoulderbolts 87, load cell 88, encoder 90, sleeve member 92, and bracket 94.

DC motor 74 performs it conventional function of rotating shaft 75 whencontrolled to do so. A mounting flange integral with DC motor 74 is usedfor fixedly mounting DC motor 74 to stator 78 of clamp 76 usingconventional fasteners (not shown). Stator 78 and rotor 80 are connectedby shoulder bolts 83. It should be appreciated that a head portion ofshoulder bolt 83 abuts stator 78; accordingly, gap 81 cannot beincreased by moving stator 78 and rotor 80 apart.

Frame 86 is fixed to the structure of robot 50. Cover 82 is fastened infixed relation to frame 86 by way of shoulder bolts 87. Accordingly,cover 82 is also fixed. Rotor 80 is also fixed to cover 82 by way of athreaded portion of bolt 83. Therefore, rotor 80, cover 82, and frame 86are fixed. However, stator 78 may move toward rotor 80, since acounterbore is formed in stator 78 for the head portion of bolt 83 justfor that purpose. Of course, motor 74 will move with stator 76, sincethey are fixedly mounted.

Screw 84 is coupled to shaft 75 by way of key 85. Therefore, when shaft75 rotates, screw 84 rotates therewith. Sleeve member 92 includesinternal threads adapted to mesh with and mate with the threads of screw84. Furthermore, sleeve 92 is slidably disposed within cover 82, suchthat rotation of screw 84 will cause sleeve member 92 to move inwardlyand outwardly relative to frame 86. Bracket 94 is fastened to sleeve 92by way of conventional fasteners.

Load cell 88 is positioned intermediate sleeve 92, and bracket 94 so asto be able to deform under load, and accordingly detect an appliedforce. Preferably, load cell 88 is an Omega (LCG) series compressionload cell, thermally compensated within a temperature range of 60° F. to160° F., requiring a 10V excitation voltage, and selected to detect therange of forces likely to be applied by welding gun 72 (in the preferredembodiment, at least 1500 pounds).

Bracket 94 is attached to welding gun 72. Thus, as bracket 94 is movedleft-to-right-to-left with respect to frame 86, the jaws of the weldinggun 72 open, close, and open accordingly.

During normal operation of actuator device 70, DC motor 74 is controlledto rotate shaft 75, which in turn causes Acme screw 84 to rotate sinceshaft 75 and screw 84 are connected by way of key 85. Rotation of screw84 causes sleeve member 92 to move in and out with respect to frame 86,thus also moving bracket 94 to open and close the jaws of welding 72 ina substantially continuous fashion to any predetermined separationdistance within the predetermined range, as illustrated by distance C inFIG. 4.

Preferably, in actual operation, device 70 is controlled to close thejaws of welding gun 72 until a "stall" condition occurs (i.e., the tipsor electrodes of gun 72 just contact the workpiece, or, perhaps, a smallforce of, perhaps 100-200 pounds of force is detected by load cell 88).

At this point, the electromagnetic clamp portion 76 is preferablycontrolled move sleeve member 92 outwardly relative to frame 86 in orderto achieve a predetermined clamping force, as detected by load cell 88.This effect is achieved by passing current through 79, causing stator78, and motor 74 to move in the direction of rotor 80. Of course, shaft75 also moves with motor 74, which causes screw 84 to also move, whichin turn causes sleeve members 92, and finally bracket 94 to also moveoutwardly to thereby apply the clamping force. The magnitude of theclamping force can be controlled by control circuitry using load celloutput as feedback to control the magnitude of the energizing currentthrough coil 79. This programmable force feature of actuator device 70permits accurate control of the resistance welding event for a varietyof welding situations, unlike the prior art combination ofcompressed-air manifold/dense pack/air cylinder 30, which is ineffectivein controlling and maintaining a desired pressure with any degree ofaccuracy.

Referring now to FIG. 6A, a side view of welding gun 72 is depicted.Before proceeding with a description of welding gun 72, it should bereiterated that welding gun 72 may be replaced by one of a plurality ofother tools in order to carryout the selected one of the plurality ofprocesses, including piercing (which usually uses plant-providedhydraulics) by way of a piercing tool, mechanical fastening, forexample, riveting using a riveting tool, forming, by way of formingdies, machining, and hemming by way of a hemming tool.

Welding gun 72 includes ribbon hose 95, electrodes 96, O-rings 97,cooling fluid inlet (feed) 98, flow split region 99 and 99 cooling fluidoutlet (return) 100. The welding gun 72 illustrated in FIG. 6 is of aconventional type available from Milco Manufacturing, Warren, Mich.,identified by Tool No. 41-858-2010, and gun ID P-PL-3272-1 (made forChrysler Corp.). This conventional weld gun is modified slightly toinclude crossover cooling path jumpers as shown by the arrows. Referringto FIG. 6A, cooling fluid enters feed port 98, and travels in thedirection of the arrow to flow split region 99. In region 99, internalchannels cause the flow of cooling fluid to be directed to the electrodeof the upper arm of gun 72, while the other portion of the feed path isfed to a first one of two channels of ribbon hose 95. As the coolingfluid circulates around the electrode 96 of the upper arm, it isdeflected and returned to split region 99, where it is directed to thesecond one of the two channels of ribbon hose 95. At region 99', thefeed cooling fluid carried in the first one of the channels of ribbonhose 95 is directed to the electrode 96 of the lower welding gun arm,while the cooling fluid carried in the second channel of ribbon hose 95is directed towards return port 100. The cooling fluid circulatingaround the lower electrode 96 is deflected and returned to return port100, where it is joined with the cooling fluid that cooled the electrodeof the upper arm of gun 72.

Referring to FIG. 6G, gun 72 includes two ports in region 99, where hose95 is attached. Thus, the above-referenced first channel of hose 95 maybe connected to a feed port in gun 72, while the second channel of hose95 is coupled to the return port of region 99 on gun 72 (carryingcooling fluid warmed by the electrode 96 associated with the upper armof gun 72). In similar fashion, gun 72 also includes a similar two portsformed in region 991 having an identical function.

Referring now to FIG. 6H, a detail of hose 95 is shown, not to scale,illustrating the connections made to the feed and return ports in FIG.6G. Holes 101 may be used for fastening hose 95 to gun 72. O-rings 97are used to provide a liquid-tight seal around the feed and return portsin region 99 of gun 72 as shown in FIG. 6G. It should be appreciatedthat jumper cables are used to carry the current to the upper and lowerarms of gun 72 and are preferably coupled to gun 72 in the areas aroundports 98 and 100. The jumper cable is mounted to gun 72 by four screws(not shown), and a one-way cooling passage associated with the jumpercable, located in the cable end connector, is adapted to be in registrywith inlet/outlet 98/100.

Referring now to FIGS. 6C and 6B, cable 66/gun 72 connections areillustrated. It should be noted at this point that three distinctembodiments may be provided. In the first embodiment, a "hip" mountedtransformer embodiment, the transformer 64 is mounted on the hip of therobot, wherein a two-way kickless cable 66 is used to couple thesecondary current from the secondary side of the transformer 64 to afixed portion of welding gun 72. In this configuration, jumper cablesare acquired for both the positive and negative polarity leads;accordingly, two jumper cables 66', as shown in FIG. 6B, are required totake the power and cooling fluid from the fixed portion of gun 72 to themovable arm portions of gun 72, as shown best in FIG. 6A (i.e., feedport 98 and return port 100). Thus, in a "hip" mounted configuration,the constructs shown in FIGS. 6C and 6B (i.e., kickless and jumpercables) would exist. However, in a "transgun" embodiment and a remotetransformer to a fixed welding gun ("hard tool"), a respective jumpercable 66' is taken directly from a respective terminal on the secondaryside of weld transformer 64 to a respective movable arm portion of gun72. Accordingly, in the "transgun" and "hard tool" embodiments, onlyjumper cable 66' (and the configuration shown in FIG. 6B) will beneeded.

Referring now to FIGS. 6B and 6D, the preferably contemplated structurefor a jumper cable 66' connection will be described.

Referring now to FIGS. 6B, and 6D, gun 72 uses a through bolt hole 102to secure jumper cable to the welding gun 72 (as opposed to four screws,with inlet/outlet in registry with cable channel embodiment). O-rings104, and 106, respectively surround the through bolt hole 102, andrespective eccentrically positioned inlet or outlet 98, 100, as bestshown in FIG. 6D. It should be appreciated that in such a configuration,a corresponding jumper cable, of opposite plurality, is provided on gun72 for carrying the opposite cooling fluid flow.

Referring now to FIG. 6E, cable 66 is shown in a exaggerated,perspective view. Cable 66 is used when workcell 40 uses a "hip" mountedweld transformer 64 (i.e., transformer 64 mounted on the robot body, noton the robot wrist near the weld gun). Cable 66 is used to internallycarry both feed cooling fluid, and return cooling fluid fromtransformer-to-gun-to-transformer. Cable 66 includes end of cable 108,first polarity conductor 110 second polarity connector 112, insulator114 between conductor 110, and 112, bolt through hole 116, and returnport 118. The conventional prior art cable carries fluid in only onedirection (i.e., from transformer to weld gun) and includes, a threadedfeed port 120 (there is also another feed port 120--not shown--similarlypositioned on conductor 112). In the prior art, the cable is insertedinto the welding gun and secured thereto by way of through bolt throughhole 116. A fitting (e.g., a manifold) would be mated to feed port 120and used to feed the cooling inlets on the welding gun. The outlets(returns) on the welding gun would be collected in a similar manifoldand returned by separate cooling hoses to the plant-provided returncooling water manifold.

In the constructed embodiment, cable 66 includes a second port formed ina position similar to port 120, but formed in conductor 112. Theinternal structure of cable 66 permits two-way fluid flow. The port 120in conductor 110 is used as a return port, while the corresponding port120 in conductor 112 (not shown) is used as a feed port. Thus, in theconstructed embodiment, the feed and return manifolds are affixed assmall fittings on cable end 108, thus requiring only small jumper hosesfrom the welding gun inlets and outlets back to these respective returnand feed manifolds.

It is preferably contemplated, however, that cable 66 include returnport 118 in conductor 110, and a corresponding port 122 in conductor112, as best shown in section in FIG. 6C. The sealing structure for thisconfiguration is identical to that shown in FIG. 6D, with a first O-ringencircling the through bolt, with a second o-ring encircling both thethrough bolt and the return or feed ports 118, 122.

FIG. 6F shows the internal cross-section construction of cable 66, whichincludes a sheath 124, a spider/spacer 126, conductors 128, an inletfeeder path 130, and a return path 132. It should be apparent thatconductors of opposite polarity are placed adjacent to each other toavoid reactions during high current carrying intervals.

Preferably, (two-way) cable 66 is obtained from Flex-Cable Company,Morley, Mich. As shown in FIG. 3, Means 53 for securing a workpiece isprovided for fixing the workpiece for industrial operations thereon.Clamp arms drawn in solid line indicate an open position, while clamparms shown in dashed-line indicate closed or clamped position. Means 53is sometimes referred to as a "tool," and include a base adapted toreceive workpiece 56, and clamps 54. Electrically-actuatedelectronically-controlled clamp 54 is an important component of workcell40. Clamp 54, as best shown in FIG. 3, is attached to a base portion ofsecuring means 53, and is responsive to a control signal from PIP 46 foractuating each of the clamps 54 to fix the position of the workpiece 56relative to the base portion of the securing means 53.

Referring now to FIG. 7A, clamp 54 includes push-type solenoid assembly134, and clamp assembly 136.

Solenoid assembly 134 is responsive to electrical control signals andpower signals for converting the electrical energy into linear motion.Solenoid assembly 134 is preferably a commercially available push-type,no pole DC solenoid, model no. S500-A3, by Trombetta Corp., Milwaukee,Wis. Solenoid assembly 134 includes longitudinal axis 138, casing 140,coils 142, plunger 144, reduced diameter bore portion 145 of plunger144, stator plate 146, enlarged through-bore portion 147 of plunger 144,return or retract spring 148, connecting rod 150, lock washer 152, andlocking nuts 154.

Plunger 144 is slidably received in a central portion of casing 140 andis adapted for motion substantially along longitudinal axis 138. Plunger144 may move from a first position corresponding to a de-energized stateof solenoid 134, to a second position corresponding to an energizedstate of solenoid assembly 134. FIG. 7A shows plunger 144 in the secondposition. In the first position, plunger 144 is displaced relativelyleftwardly of that shown in FIG. 7A along axis 138. Spring 148 isdisposed within an enlarged portion 147 of plunger 144. Spring 148 is incompression in both the first position, and the second position ofplunger 144. Spring 148 may have an associated free length of sixinches, while the enlarged diameter bore portion 147 may have a lengthof three inches. Thus, when solenoid assembly 134 is in a de-energizedstate, the force of spring 148 urges plunger 144 to the first position.

Connecting rod 150 is preferably constructed of non-magnetic material,preferably non-magnetic stainless steel. Rod 150 is fastened to plunger144 by way of threads in reduced diameter bore portion 145. Rod 150 isfurther fastened to plunger 144 by way of washer 152, and nuts 154.Since plunger 144 is connected to rod 150, travel of plunger 144 to thefirst position is limited by the permissible travel of rod 150, which isdefined more clearly below in the discussion of clamp assembly 136.Likewise, travel of plunger 144 to the second position is also limitedby the permissible travel of connecting rod 150, which is more clearlydescribed below.

In the de-energized state of solenoid assembly 134, plunger 144 ispositioned leftwardly relative to the position shown in FIG. 7A, dueprimarily to the force applied by spring 148 to plunger 144, as limitedby the permissible travel of connecting rod 150.

In an energized state, plunger 144 moves rightwardly of the de-energizedposition along axis 138 in the direction of stator plate 146 to reachthe second position. Movement to the second position causes furthercompression of spring 148. Travel to the second position is limited bythe permissible travel of connecting rod 150.

Upon de-energization, spring 148 expands, thus causing plunger 144 toreturn to the first position moving rod 150 leftwardly along axis 138.

Clamp assembly 136 includes first axis 155, housing 156, through-bore157 (FIG. 7E) formed about axis 155 cover plate 158, fastener 159 (bestshown in FIG. 7C), clevis 160, T-channel or raceway 161 (best shown inFIG. 7C), link 162, first pin 164, shaft 166, extending portion 167 ofshaft 166 (best shown in FIG. 7D), second pin 168, outer periphery 169of shaft 166, stop block 170 slot 171 of shaft 166, contact bracket 172,clamp arm 174 (shown in phantom), wear plate 176, a pair of slide racks178 (best shown in FIG. 7C), fasteners 179 (best shown in FIG. 7C), faceplate 180, a pair of proximity switches 182, and bearings 184.

Housing 156, as shown in FIGS. 7A-7E, provides a general base structurefor operation of clamp 54. As best shown in FIG. 7E, housing 156includes a through bore 157 sized to accommodate shaft 166 therein, asshown in FIG. 7D.

Cover plate 158 is fastened to housing 156 by way of conventionalfasteners, as best shown in FIG. 7C. Cover plate 158 excludescontaminants from entering the interior portion of clamp 54 from thetop. As shown in FIG. 7C, T-shaped wear plate 176 is fastened to coverplate 158 by way of fastener 159. Thus, wear plate 176 is fixed relativeto housing 156.

Clevis 160, as best shown in FIGS. 7C and 7D, includes a correspondinglyshaped T-shaped raceway 161 formed on a top portion thereof, raceway 161being defined partially by a pair of slide racks 178 fastened to clevis160 by way of fasteners 179. Clevis 160 is slidably disposed on wearplate 176 for motion in either direction along axis 138. In oneembodiment, wear plate 176 and raceway 161 form the means for slidablymounting clevis 160 for motion relative to housing 156 along axis 138.Connecting rod 150 threadedly engages clevis 160. Thus, plunger 144moves in unison with clevis 160 along axis 138 by way of connecting rod150. Accordingly, clevis 160 also assumes the first position(de-energized state of solenoid assembly 134), and the second position(corresponding to an energized state of solenoid assembly 134). Clevis160 is shown in the second position in FIG. 7A.

Link 162 is rotatably connected to clevis 160 by way of pin 164. Link162 is shown in a first position (in phantom-FIG. 7A) corresponding to adeenergized state of solenoid assembly 134. Link 162 is shown in solidline in FIG. 7A corresponding to an energized state of solenoid assembly134.

As best shown in FIG. 7D, shaft 166 is disposed within bore 157 ofhousing 156, and is adapted for rotation therein about axis 155. Shaft166 is generally cylindrical in shape, and is coupled to link 162 by wayof pin 168. Shaft 166 further includes a portion 167 extending outwardlytherefrom, as best shown in FIG. 7B. Portion 167 serves two purposes.First, a surface portion of extension 167 is used, in cooperation withstop block 170, to limit the clockwise rotation of shaft 166 withinhousing 156, as best shown in FIG. 7A. Secondly, extension 167 providesa means for fastening clamp arm 174 to clamp 54. Shaft 166 also includesa slot 171 extending radially inwardly from outer periphery 169. Clevis160 is disposed in slot 171 (FIG. 7C).

Stop block 170, in addition to the stop function previously described,also serves to retain and position shaft 166 within housing 156.

Contact bracket 172, best shown in FIGS. 7A, and 7B, is provided formaking contact with proximity switches 182. Contact bracket 172 isfastened to shaft 166 for rotation therewith. Accordingly, in the secondposition (corresponding to the energized state of solenoid assembly134), contact bracket 172 contacts the lower proximity switch, as viewedin FIG. 7A. This corresponds to a clamped or closed position of clamp54. When solenoid assembly 134 is de-energized, contact bracket 172 isadapted to contact the upper proximity switch as shown in FIG. 7A,indicating t hat the clamp is in an open or unclamped position. Itshould be appreciated that proximity switches 182 may take a variety offorms, that are recognized as conventional by those of ordinary skill inthe art.

Bearing 84 is preferably a Rulon standard load bearing type DRS-0609-4.

Associated with clamp 54 is a rectifier/driver module (not shown)selected to match the operation of solenoid assembly 134. Therectifier/driver module is commercially available, and preferably isModel Q517-A1, from Trombetta Corporation. The rectifier/driver modulereceives as an input 120 volts AC. The rectifier/driver output isdual-state: for approximately 0.5 seconds after 120 volts AC is appliedto the input, the rectifier/driver module outputs approximately 108volts DC to the solenoid assembly 134 (connections not shown). This highvoltage is required in order to overcome the high inertia involved inmoving the plunger from a rest position. After the 0.5 second intervalhas expired, the rectifier/driver module automatically decreases itsoutput voltage to solenoid assembly 134 to approximately 15 volts DC, alevel sufficient to "hold" or maintain solenoid assembly 134 in anenergized state.

In the constructed embodiment, each clamp in the proximity of tool 53has a 6-conductor cable interfaced thereto. The rectifier/driver moduleassociated with each clamp is housed not proximate the clamp itself, butrather, in the PIP 46. The 6 wires leading from each clamp are asfollows: (1) a positive (+) DC voltage lead; (2) a negative (-) DCvoltage lead; (3) a "hot" power lead that is split at the clamp andprovided to each of the 2 proximity switches 182; (4) a ground lead; (5)a lead associated with a first one of the switches 182; (6) a leadassociated with the other one of the switches 182. These 6 leads aretaken from clamp 54 to the PIP 46.

The first 2 leads (DC power for solenoid assembly 134), are wired to theoutputs of a respective rectifier/driver module. Leads (3) and (4) areconnected to power. Leads (5) and (6) are connected to various I/Opoints. The PLC or PC (hereinafter to mean computer 42 with PLCreplacement software) is operative to apply, in accordance with apreprogrammed control strategy, 120 volts to the input of therectifier/driver. The other 2 leads from the proximity switches arecross connected in the PIP 46 to the appropriate I/O ports for use bythe control program of the PLC or PC.

It is preferably contemplated, however, that clamps 54 be connected in amultiplexed, daisy-chain type arrangement. In particular, intelligentI/O modules are known in the art for implementing such a multiplexingscheme. For example, one such device, commercially available, is aserial multiplexer module (SPX series) by APC Seriplex™, Jackson, Miss.In general, the Seriplex module operates as follows. Each module isprogrammed with an address and a command. A 4-conductor bus (clock,data, and power leads) is then daisy chained to each clamp having aprogrammed module. When an address is applied to the bus (accomplishedby raising the data line during a time slot of the clock correspondingto the desired address), all devices having the selected address performthe preprogrammed command. So, for example, the I/O module associatedwith clamp 54 may be preprogrammed to close a rely associated therewith(i.e., one of the available commands) operative to apply 120 volts AC tothe above-described rectifier/driver module to thereby actuate theassociated clamp 54. In this fashion, the wiring requirements aresignificantly reduced. A bus control (also commercially available, forexample, a PC interface card model SPX-PC-INTF from APC Seriplex) needonly apply the address of the clamp desired to be actuated to the bus.This procedure can be repeated in rapid succession for each addressassociated with each clamp to close each clamp associated with tool 53.

Referring now to FIG. 7A, a description of the operation of clamp 54will now be set forth. In a de-energized state, spring 148 is operativeto move plunger 144 to the first position, thereby also movingconnecting rod 150 leftwardly, which in turn moves clevis 160leftwardly, which in turn moves link 162 to the first position, a sindicated in FIG. 7A in phantom line. Since link 162 is pinned to shaft166, shaft 166 is rotated to a corresponding first position. The clamparm 174 is thus in an open or unclamped position.

To actuate clamp 54, a control (PLC or PLC replacement system) appliesan activate signal to a I/O port in PIP 46. In the constructedembodiment, 120 volts AC is then applied to the rectifier/driver module(not shown). The rectifier/driver module then applies approximately 108volts DC to the positive and negative leads which are then taken to,over various cabling, to solenoid assembly 134 of clamp 54. As coils 142are energized, plunger 144 moves relatively rightwardly along axis 138,thus further compressing spring 148. Connecting rod moves with plunger144 thus causing clevis 160 to move away from the first positionlinearly along axis 138. Clevis 160 is guided in its travel by way ofthe T-shaped keyway 161, and corresponding T-shaped wear plate 176.Since link 162 is rotatably pinned by pin 164, and is further pinned toshaft 166 by way of pin 168, linear motion of clevis 160 is translatedto rotational movement of shaft 166. Shaft 166 continues to rotateclockwise (as viewed in FIG. 7A) until portion 167 of shaft 166 abutsstop 170. Clevis 160, and plunger 144 are now in the second positionwherein the workpiece is clamped, as shown by dashed-line clamp arms inFIG. 3. After approximately 0.5 seconds, the rectifier/driver moduledown grades the applied voltage to approximately 15 volts DC to "hold"the plunger 144 in the second position.

To open the clamp, the solenoid assembly 134 must be de-energized. Thisis achieved under control of the PLC or PLC replacement system, whichdiscontinues input power to the rectifier/driver module. Therectifier/driver module, in turn, discontinues energizing power tosolenoid assembly 134. Plunger 144 begins to move from the secondposition to the first position under the force applied by spring 148. Asplunger 144 retracts, so does connecting rod 150, and clevis 160. Asclevis 160 moves leftwardly, relative to the position shown in FIG. 7A,link 162 also moves from the position shown in solid line to theposition shown in phantom line in FIG. 7A. Shaft 166 is accordinglyrotated counterclockwise, and the clamp is therefore opened.

An important feature of clamp 54 relates to link 162. In a clamped(second) position, forces applied to clamp arm tending to open clamp 54are directed generally upwardly, as indicated by the arrow labelledForce. The force is generally perpendicular to the direction of travelof clevis 160, rod 150, and plunger 144. Therefore, once activated,clamp 54 is mechanically locked--and therefore able to withstand forces(opening) generally greater than the force developed by solenoidassembly 134. This feature permits use of a smaller solenoid than wouldotherwise be required if the solenoid had to develop sufficient force todirectly counteract any unclamping/opening forces.

As indicated above, it is preferably contemplated that the clamps be busmultiplexed by way of conventional "smart chip", to enable a reductionin wiring. In this embodiment, the method of securing a workpiece 56 byselectively actuating one of a plurality of the electrically-clamps 54through the resulting data highway includes the following steps. First,each clamp is assigned an address on the bus. Some systems require thatthis address be unique. Other systems, such as the Seriplex methology,permit the same address to be used by more than one device. The nextstep involves selecting one of the clamps for actuating. Next, thecontrol signal on the bus must be formatted to include the addressassociated with the clamp selected in the prior step. In the APCSeriplex system, the formatting step preferably takes the form ofraising the data lead on the bus to a logic high level during a timeslot of the clock corresponding to the desired or selected address. Thenext step involves broadcasting the control signal to each clamp throughthe data highway or bus. Finally, providing actuation power to theaddressed clamp. The APC Seriplex system performs this step by closing arely, which may be externally configured to supply the necessary powerto the clamp rectifier/driver module.

Referring now to FIG. 8, actuator control 58 includes selector switch186, 2-axis servo controller 188, brushless amplifier 190, DC brush typeservo amplifier 192, terminal blocks 194, 196, and load cell display198.

Actuator control input device 59 may be used with a plurality ofcontrollers 188; accordingly, selector switch 186 is provided forimplementing the flexibility necessary for such a configuration.

Controller 188 of control 58 is provided for controlling the DC motor74, and actuator clamp 76 portions of actuator positioning and clampingdevice 70. Controller 188 is conventional and commercially available,and may be, for example, model 6250 from Parker Hannifin Corporation(Compumotor), Rohnert Park, Calif. The controller 188 is a sophisticateddevice which may be programmed to control both the position of sleevemember 92 (see FIG. 5) by way of encoder 90 data, and thus the jawopening (i.e., tip separation distance) of welding gun 72, and further,to control the clamping force applied by welding gun 72 using load cell88 feedback data. These programs may take the form of "schedules" thatare designed and tuned on input 59, and downloaded into controller 188for run-time retrieval and execution. Amplifier 190 is conventional andcommercially available, and may be a Reliance model BDC25L, availablefrom Electro-Craft®, Edan Prarie, Minn. Amplifier 190 is a brushlessamplifier and is responsive to the command signals generated bycontroller 188 in accordance with its program in order to provide drivesignals to motor 74 by way of terminal block 194.

Amplifier 192 is also conventional and commercially available, and maybe model series 30A-AC model 16A20-AC, available from Advanced MotionControls, Camarillo, Calif. Brush type servo amp 192 is responsive to aclamp analogue command voltage control signal generated by controller188 in accordance with its program for generating corresponding drivesignals by way of terminal block 196 to magnetic actuator clamp 76.

Actuator control input 59 is provided for programming controller 188 inaccordance with a predetermined control strategy. For example, and asindicated above, actuator device 70 may be programmed to maintain apredetermined separation distance between the electrodes 96 of weldinggun 72 when robot 50 moves assembly 52 from weld 1 position to weld 2position, the separation distance being selected just to avoid anyobstruction. Further, controller 188 may be programmed to cause weldinggun 72 to clamp to a predetermined force, as detected by load cell 88.Moreover, kinematics related to the closing, clamping, and opening ofwelding gun 72 may be controlled on a force-vs-time basis (a so-called"profile"). A software program may be used to initialize and program theschedules into controller 188 and preferably, in the input mechanism isa software program named Motion Architect™, version 3.1, available fromParker Hannifin.

Weld control 60 is provided for controlling timing, duration, percentheat, percent current, current, and many other factors that are wellknown to those of ordinary skill in the art that are relatedparticularly to the weld event itself. Weld control 60 accomplishes thisend by selectively connecting a power source (e.g., 440 volts) acrossthe primary side of transformer 64. The transformer 64 converts thisrelatively high voltage, low-current, into a very high current lowvoltage across the secondary side of transformer 64. When the powersource is applied to transformer 64, relative to the power sourcevoltage, affects the character of the weld. Weld control 60, also knownas a weld timer 60, are conventional units and are commerciallyavailable, and may be model number 700-S, part number 970-0161 (for therobot 50 weld gun), and part number 970-0162 (for the fixed weld gun"hard tool" associated with the clamping tool 53), available from Medar,Farmington Hills, Mich. In the preferred embodiment, the weld controlsare purchased so as to comply with Chrysler welding spec WC 2.1.Further, the hard gun weld control (not illustrated) is a 300 amp, 50%duty cycle air cooled SCR configuration. The primary power electronicsin weld control 60 are power switching devices (known as a contactorstructure), generally selected to be silicon-controlled rectifiers(SCRs). For the weld control 60 shown, the SCR's selected may beidentified as part number PAAA7T100718BT, available from Darrah. Inaccordance with the present invention, no cooling water is used to coolthese power electronic devices. Rather, they are air cooled through theuse of heat sinks. The heat sink used in the preferred embodiment is aDarrah, model A7. The current carrying limit of the SCR's as used inconjunction with the heat sink, is specified at 420 amperes, continuous.This limit has been found to be satisfactory in the preferred embodimentillustrated in FIG. 3.

Transformer 64 is a conventional design, and may be a 200 KVA modelnumber G446200KL2164W, from Roman Manufacturing Incorporated.Transformer 64 includes a first inlet and outlet to define a coolingfluid path. In one embodiment ("hip mount"), cable 66, shown in FIG. 6Eis used and short jumper hoses are used to link the transformer coolingwater inlet/outlet ports to the feed/return ports 120 of cable 66. It ispreferably contemplated that a mounting bracket for transformer 64 likethat shown in FIG. 6C and designated as 72 be adapted for use inconjunction with welding transformer 64 such that the aforementionedshort jumper hoses can be eliminated. In other words, it is preferablycontemplated that transformer 64 be fitted with a bracket of the samedesign as shown for the gun 72 illustrated in FIG. 6C.

FIGS. 9A, 9B, and 9C shows various views of chiller 68. The main featureof chiller 68 lies not primarily with the function that it performs;this is generally conventional. But rather, in the packaging orcompactness of its design, which permits placing the chiller underneathrobot 50 and workcell 40. In a preferred embodiment, the chiller is 40"square, and 201/2" in height. Approximate weight 480 lbs. The chiller 68is associated exclusively with workcell 40, thus obviating the need forreliance on plant-provided cooling water, as in prior art workcell 10.The chiller functions to remove heat from the cooling fluid, and provideflow energy to circulate the cooling fluid throughout the workcell 40.Chiller 68 includes compressor 200, electrical box 202, caster 204,air-cooled condenser 206, tread 208, process pump 210, evaporator 212,reservoir 214, sight glass 216, pressure gage 217, a feed port 218 tofeed cooling fluid to the robot manifold 69, and a return port 219 forreceiving cooling fluid from the robot manifold 69. In the preferredembodiment, the chiller 68 is a model PCAQ-3-NF-460 from AlphaEnvironmental Refrigeration Company, Rochester Hills, Mich.

In the preferred embodiment, compressor 200 includes a 3 horse power,1800 RPM, 6.7 amp electric motor. Air-cooled condenser 206 includes anair-cooled condensing unit, part number F3AD-A301-TFD-001 from Copeland.Process pump 210 may be a 2 horse power, 3450 RPM, ODP part numberLCAA-2035 from G & L. The process pump is provided for generating a headfor circulating the cooling fluid through workcell 40. In the preferredembodiment, a flow rate of 10 gallons per minute (GPM) at 60 psi hasbeen found to be satisfactory.

Evaporated 212 may be a braze plate evaporator, part CH-3A from FlatPlate. Reservoir 214 is preferably a 10 gallon stainless steelreservoir, part number 10SS from Alpha Environmental RefrigerationCompany.

Referring now to FIG. 10, a functional diagrammatic and schematicdiagram view of chiller 68 is depicted. Chiller 68 further includes anover temperature thermostat 220, a freeze thermostat 222, an accessvalve 224, an expansion valve 226, a liquid line solenoid valve 228, asolenoid coil 230, a liquid line sight glass 232, a filter drier 224, aliquid line valve 236, a pressure relief valve 238, a pair of condenserfan motors 240, condenser fan blades 242, a pressure control 244, a hotgas service valve 246, a hot gas solenoid valve 248, and a hot gasbypass valve 250. The components are conventional and commerciallyavailable and operate in a manner known to those skilled in the art.

Referring now to FIG. 4, the closed loop self contained cooling systemwill be described in total for a "hip mount" embodiment. Chiller 68provides a continuous supply of cooling water at a feed port. The feedport 218 is routed internal to robot 50 to manifold 69. Manifold 69includes 2 feed hoses therefrom, and 2 return hoses. One feed hose andone return hose is used solely for weld transformer 64 and are connectedto the first inlet and outlet, respectively. The second set offeed/return hoses of manifold 69 are routed to cable 66 proximatetransformer 64. Cable 66 includes internal feed and return paths. In theconstructed embodiment, cable 66 mounts to transformer 64 electrically,while ports 120 (feed and return), as described above, receive the feedand return hoses from manifold 69, respectively. At the far end at gun72, cable 66 terminates on a fixed portion of gun 72, and ports 120(feed and return) of cable 66 are fitted with manifolds to feed gun 72,as described above.

It is preferably contemplated, however, that the advanced sealingtechnology described be used.

As best illustrated in FIGS. 6B and 6C, portion 72 shown in FIG. 6Crepresents the fixed portion of gun 72 (using the internal channels 118,122) in the preferred embodiment shown in FIG. 3. Jumper cable 66 thentakes the cooling fluid to the movable arm portion of gun 72.

Referring now to FIG. 6A, the jumper cable is fastened to the movablepart of gun 72 at inlet 98. Fluid flow feed cooling water is then splitinternally in gun 72. A first portion of the cooling water is directedthrough a first channel of ribbon hose 95 from the upper arm to thelower arm and further then directed to the lower arm electrode and thendeflected back to outlet 100. The second portion of the split feedcooling water is directed to the electrode 96 of the upper arm,deflected, and then fed through a second channel in ribbon hose 95 tothe lower arm of gun 72, and is further directed internally to outlet100 to be joined with the first portion of the feed cooling water. Thecombined outlet stream from outlet 100 defines the return cooling water.Return cooling water from outlet 100 is then channeled, by a Jumper 66',back to the fixed portion of gun 72, where it is then directed to thereturn path in cable 66 (as shown in FIG. 6C), and thence back to thereturn feed hose at the end of cable 66 proximate weld transformer 64,as shown best in FIG. 4. The return cooling water is then transportedinto manifold 69 and returned to chiller 68. It is preferablycontemplated that the four hoses of manifold 69 be reduced to one feedhose/one return hose as follows. Feed hose to transformer 64 inlet.Transformer 64 splits feed: one portion to cable 66 connected totransformer 64 by structure of FIG. 6C; a second portion to cooltransformer 64 itself. Return fluid from gun 72/cable 66 is joined withsecond internally to transformer 64 to form one return feed to manifold69. It should be appreciated that the host of cooling water feed andreturn hoses, manifolds, etc. have been eliminated by a workcell inaccordance with the present invention, as shown generally in FIGS. 3 and4.

Referring now to FIG. 11, the steps performed by the preferredembodiment of the present invention will now be described. In step 260,the PLC or PLC replacement system (PC 42 with PLC replacement software)first determines whether several preliminary requirements have been met.These preliminary requirements include checking whether a part presentsignal is active, whether all of the clamps 54, as commanded, haveclosed, as indicated by respective proximity switches 182 and whether aplurality of other initialization requirements (e.g. safety screenunbroken, etc.) have been met.

In step 262, the PLC or PLC replacement commands robot controller 48 toinitiate a cycle. A "cycle" is a series of welds that may be requiredfor a particular workpiece(s) under process.

In step 264, the weld number, represented by the variable I, is set to1.

In step 266, the robot controller controls robot 50 to position weld gun72 for weld I. It should be appreciated to those skilled in the art,that the position for each one of the I welds has been preprogrammedinto robot controller 48 by way of robot controller input 49. Robotcontroller 48 will not proceed with execution until robot 50 has movedto a position corresponding to weld I.

In step 268, robot controller 48 sends a command to actuator control 58to activate actuator assembly 70. The term "activate" means to controldevice 70 such that welding gun 72 closes and applies a predetermined,programmed clamping force associated with weld I.

In step 270, robot controller 48 sends an initiate weld command to weldcontrol 60 when an okay to weld (OTW) signal is received from actuatorcontrol 58. Actuator control 58 sends out an okay to weld signal when ithas completed its preprogrammed closure of welding gun 72, and hasapplied the predetermined force.

In step 272, robot controller 48 sends an okay to open (OTO) command tothe actuator control 58 when an end of weld (EWD) signal is receivedfrom weld control 60. Weld control 60 sends the end of weld signal whenit has completed the programmed weld schedule for weld I. It should beappreciated that a conventional weld control, such as weld control 60may be programmed with a variety of so-called weld schedules, eachschedule defining a unique weld event (percent heat, number of amperes,number of cycles, etc.). It should be further appreciated that in step270, part of the initiate weld command includes selection of aparticular weld schedule, which is selected in advance when robotcontroller 48 is being programmed. Thus, a "cycle" includes not onlyweld gun position information for each one of the I number of welds, butalso weld schedule information associated with each one of the I numberof welds, but also an actuator schedule defining a separation distanceof electrodes 96 prior to welding, a force-vs-time profile for theclosure of gun 72, the clamping force, and a mid separation distance,optimized to decrease the amount of time needed to clamp down during thenext weld (while avoiding obstructions).

In step 274, robot controller 48 waits to receive an okay to move (OTM)signal from the actuator control which occurs when the actuator control58 has caused actuator assembly 70 to move the jaws of welding gun 72 toa predetermined mid separation distance in order to clear anyobstruction to get to the next weld position.

In step 276, robot controller 48 checks to see whether there are anyremaining welds to be accomplished in the current cycle. If there aremore welds, execution occurs through step 278, wherein the weld counteris incremented by one, and execution resumes again at step 266-276 forthe next weld position. However, if all the welds have been made, thenrobot controller 48 sends an end of cycle signal to the PLC, or PLCreplacement system (PC 42 plus PLC replacement software).

Referring now to FIG. 12, the internal operation of actuator control 58,in conjunction with actuator assembly 70, and welding gun 72 will nowdescribed. In step 282, general initialization procedures are performed.

In step 284, control 58 causes the electrodes 96 of gun 72 to touch todetermine an absolute 0 position, as indicated by encoder 90 shown inFIG. 5. Gun 72 is then fully opened.

In step 286, the status of certain safety and interface bits aremonitored and necessary communication with other controls (such as robotcontroller 48) occur.

In step 288, a test is performed to see whether a close to part has beenreceived, indicating that the workpiece has been clamped into position.

In step 290, a schedule is read from robot controller 48 interface. Asindicated above, the schedule contains specified information for eachweld, including but not limited to, clamping force, tip distance, foreach weld, force-vs-time profile, etc.

In step 292, appropriate parameters corresponding to the receivedschedule are initialized.

In step 294, subroutines are executed using the schedule number to setthe number of welds, as well as the above-mentioned parametersassociated with each weld, including clamping force and tip distance.

In step 296, the welding gun 72 is closed to a prep distance associatedwith the current weld point. This prep distance is predetermined tooptimize closure time.

In step 298, a test is performed to determine whether robot controller48 has sent the activate command. If not, predetermine safety bits areagain checked in step 300, and a test is again performed.

In step 302, the gun has closed to 0 when the activate command isreceived from robot controller 48.

In step 304, the predetermined clamping force is applied and held for apredetermined time associated with the current weld.

In step 306, actuator control 58 sends an OTW signal to robot controller48.

In step 308, a test is performed to determine whether the OTO signal hasbeen received. At this point, robot controller 48 is commanding weldcontrol 60 to initiate and complete a weld in accordance with apredefined and preselected weld schedule associated with the currentweld.

In step 310, predetermined safety bits are again checked in step 310.

In step 312, once the OTO signal has been received by actuator control58, the tips 96 of gun 72 are open to a mid separation distanceassociated with the current weld. It should be appreciated that thisdistance has been selected, based upon the geometry of the workpiece,and the window in which the robot wrist may travel, in order to optimize(i.e. reduce) the time it takes to travel to the next point and closethe gun for the next weld.

In step 314 actuator control 58 sends an okay to move (OTM) signal torobot controller 48.

In step 316, actuator control 58 checks to determine whether it hasreceived an out of part (OOP) signal, indicating that the workpiece orpart has been completely processed, and is being moved to anotherworkcell.

In step 318, again, certain safety bits are monitored and checked andany required action is taken.

In view of the foregoing, the advantages of a workcell in accordancewith the present invention should be apparent. Eliminating all of thecompressed air hoses, and substantially eliminating all of the loosecooling water hoses, by eliminating reliance upon plant-providedfacilities, contributes significantly to improve reliability and uptime. Further, by eliminating the above-mentioned hoses, workcellvariability (i.e. workcell-to-workcell) is significantly reduced, thusmaking the job of programming the various controls, especially movementsof robot 50, significantly easier, and therefore more cost effective. Inthis connection, elimination of the above-mentioned hoses also provideslarger windows for which the robot arm may pass, thus further easing thetask of programming the movement of robot 50. Material cost is furthersignificantly reduced, in shear terms, by eliminating various pipes,hoses, manifolds, dense packs, etc. Further, the labor involved toinstall the above-mentioned components has accordingly also beeneliminated. Not only is cost reduced, and maintainability and up timeincreased, but performance of a workcell in accordance with the presentinvention is also significantly improved. Particularly, actuator control58, actuator assembly 70 and welding gun 72 cooperate to provide avirtually infinite variety of tip separation distances, and clampingforces. This flexibility permits not only improved processing speed(i.e., the time required to make a weld, move on to the next weld, andcomplete processing of the workpiece), but further, also provides thenecessary control, by way of accurately providing clamping force, tomore closely control the welding event, thus improving the quality ofwelds, and perhaps, reducing the number of welds required to be made ona particular workpiece.

The preceding description is exemplary rather than limiting in nature. Apreferred embodiment of this invention has been disclosed to enable oneskilled in the art to practice this invention. Variations andmodifications are possible without departing from the purview and spiritof this invention; the scope of which is limited only by the appendedclaims.

We claim:
 1. An improved resistance welding system havingself-contained, closed loop cooling, comprising:a chiller associatedexclusively with said welding system for removing heat from coolingfluid, said chiller having a feed port and a return port for said fluid;a welding transformer having a first inlet and outlet to define a firstcooling path, said first inlet being coupled to said feed port, saidfirst outlet being coupled to said return port of said chiller; a cableconnected to a secondary side of said transformer at a first end forcarrying secondary welding current, said cable including means coupledto said chiller for internally bidirectionally transferring coolingfluid; and a welding gun connected to a second end of said cable andhaving a pair of electrodes for applying said secondary welding currentthrough a pair of workpieces, said welding gun including means forreceiving, circulating, and returning cooling fluid to said chiller. 2.The system of claim 1 wherein said welding gun includes a plurality ofinternal channels for cooling said electrodes which derive from a commoninlet and rejoin at a common outlet.
 3. The system of claim 1 whereinsaid transformer includes a primary side that is selectively connectedthrough an air-cooled contactor structure to a power source.
 4. Thesystem of claim 1 wherein said means for receiving, circulating, andreturning cooling fluid is internal to said welding gun.